1. Field of the Invention
The present invention relates to the art of laser information recording and more particularly to a laser information recording medium with an improved recording layer of organic dyes.
2. Description of the Prior Art
A number of attempts have been made to fabricate laser information recording media using organic dyes. The principle behind the information recording in these media is based on geometric variations of the media caused by application of heat which is generated by the absorption of a laser beam by the dye. However, this type of medium makes it difficult to protect the recording layer sealingly from opposite sides in practical applications. To avoid this diffulty, it is necessary to adopt a complicated structure such, for example, as an air sandwich type structure which in turn makes the recording medium complicated. In these information recording media, it is essential that the geometric variations be in the form of spots having a uniform shape and a fine size. This recording principle used in known recording media is opposite to a tendency toward high density recording which has become increasingly important in recent years. In addition, in order to cause the geometric variations in the medium, it is essential to provide energy for melting and vaporization at a minimum value. The geometric variations involve release of dye molecules from the recording pits, which process does not proceed reversibly.
When organic dye molecules, e.g., cyanine dye molecules, are highly concentrated in an aqueous solution, there appears an absorption band or peak which has a large absorption intensity at a longer wavelength than is the case of a single molecule absorption band and has a very narrow half-amplitude level. There is also an absorption band of a single molecule of the dye, an absorption band of the dimer form at a shorter wavelength, and an absorption band of polymolecular aggregates. This absorption band is called the J-absorption band and is known to derive from aggregates of dye molecules called J-aggregates.
We have found that the J-aggregate dissociates by application of heat and the absorption spectra before and after dissociation vary significantly from each other. We have already proposed in Japanese Patent Application No. 59-149040 a laser information recording medium which comprises a recording layer made of a cumulative film of J-aggregates which are obtained from a cyanine dye of the following formula (I) and arachic (arachidic) acid used as a film-forming material. ##STR1## However, the yield of the J-aggregates in this system was not necessarily satisfactory.